Duck production in the Mekong Delta and taro (Colocasia esculenta)
foliage as feed supplement

Nguyen Tuyet Giang

Department of Animal Husbandry and Veterinary Medicine,

Angiang University, Vietnam

Duck production in Vietnam

Vietnam is a country situated in Southeast Asia with a population of
85.79 millions and an
area of 331,114 km2.
Vietnam has a paddy rice culture and approximately 70% of the population lives
in the countryside, and 90% of households raise poultry. According to Doan Xuan
Truc (2001), Vietnam ranks 5th in ASEAN and 47th in the world in poultry meat
and egg production. Traditionally, poultry are kept in small scale system, in
the back yard and close to farmers’ houses. As study of Hall et al. (2006)
showed that small scale farmers in Vietnam keep poultry for cash income and
food, and raising poultry is a form provides a small proportion of total
household economic activities (5-10%) compared to more intensive enterprises
(20-85%). According to a FAO (2004) classification, poultry production
(including ducks) diversifies into sectors depending on the management and
marketing system: industrial integrated system (integrated farms with various
components are managed under high biosecure procedures); the industrial sector
(commercial poultry production system with moderate to high biosecurity and
birds/products usually marketed commercially; birds are kept indoors, completely
inhibited from contact with other animals); semi-commercial sector (low to
minimal biosercure level in which birds are housed in cages; open sheds allowed
spending time outside the shed) and the sector of village or backyard
production, which is under or without biosecurity, and birds and products are
sold or consumed locally.

In Vietnam, there is also another standard using herd
size as standard to classify the poultry sector, which can be found in both
rural and industrial sectors. There are 400,000 small and medium scale farms
with 50 to 5000 head of poultry and at least 8 million households use small
scale systems with less than 50 poultry head. Vietnam has many advantages
to enhance duck production. Firstly, the natural resources with appropriate
climate conditions, a large number of rivers, as well as canal networks, are
suitable for developing duck production. Vietnamese farmers have a long
experience of raising ducks; they can utilize local feed sources that are cheap
and available through out the year. Vietnam is ranked 4th in the world, after
China, France and Thailand (Doan Xuan Truc 2001) in duck production. Products
from duck production are meat, eggs and feathers. In addition, salted duck eggs
have become a product into some Asian markets in recent years. The duck is a
water fowl that can easily adapt to different environments, with or without
water. Ducks are raised mostly for meat and egg purposes. Farmers like to keep
ducks because of the low investment, utilizing local materials for housing;
ducks are well resistant to common diseases and grow well on locally available
feed resources. Ducks are easily raised with low nutritional feed inputs but
they rapidly bring benefits, with short life cycle, high growth development and
productivity. In addition, ducks can be seen widely in the rural and remote
areas where farmers are stakeholders, although they are facing handicaps in
accessing to appropriate technologies, information, market and help services
(Shan-Nan Lee 2009).

Among the agroecosystems, the Red River Delta, Mekong River Delta and North East
regions accounted the highest proportion of poultry (Desvaux Stephanie et al.
2008). According to Bosma et al. (2005), since livestock requires less and lower
land quality than cultivated plants, farmers invest more in livestock
activities, raising ducks or chickens, fish or pigs, buffaloes or cattle, for
example. In fact, raising ducks for eggs involves a risky investment for the
smallholder in the Mekong Delta. In contrast to chickens, ducks may lay eggs
everywhere, and then need to be fenced and restricted by nets, also in order to
keep the birds safe at night. Also a bedding of straw or rice husks should be
prepared to protect the eggs from breaking. For intensive systems, the flock
size varies from about 500 to 5000 ducks. Landless farmers generally start with
smaller flocks and expand slowly in order to minimize the investment and labour.

Raising systems

Scavenging free range system

Vietnamese farmers have a long experience of scavenging ducks in the backyard or
garden. Complete scavenging systems or semi-scavenging are most suitable for
most local duck breeds (Nguyen Thi Kim Dong 2005). Most stakeholders apply this
system because they can start with a small size flocks (5-50 ducks) in the
backyard or garden. Although this system is distinguished by low feed offer,
with or without housing, farmers can profit from products they get (meat and
eggs). If predators are a problem at night, the open areas or pens can be
covered by inexpensive net or wire mesh (Dean and Sandhu 2006). Ducks can
effectively be fed home wastes or cheap by-products (such as rice bran or broken
rice) 2-3 times per day; they also have free access to other feed sources in
rivers, pond or areas of the rice fields (Bui Xuan Men 1996).

Integrated systems

In the Mekong Delta, farmers use many traditional ways to raise ducks, of which
the integrated systems are the most common. Bui Xuan Men (1996) mentioned that
besides scavenging, a very traditional system, which is not very profitable.
Ducks can be raised along with growing rice but do not harm the plants in the
early stage of growth, before flowering. After the brooding stage (at more than
1 week of age), ducklings are let into the rice fields (20 days after
transplanting until flowering). Ducklings can find and consume snails and
insects in the rice field. While scavenging, ducklings can consume weeds, swim
and stir the mud around the plant roots without harming the rice plants. Ducks’
excreta also fertilize and stimulate rice growth. In this way, farmers can save
money for pesticides, herbicides as well as chemical fertilizer. The second
model is raising ducks in the post-harvest rice fields. Commonly, both laying
and meat type ducks are reared. Above 3 weeks of age, ducklings can consume
whole rice grains. After harvesting, ducks can scavenge in the rice field
leftover or fallen rice grains, insects, shellfish, frogs, weeds, fish and water
plants. Today, varieties of high yielding rice are preferred, and after the
harvest just takes, it only takes a few days to start a new crop. In such
circumstances, this system becomes less flexible. Ducks can also integrate with
fish (Le Hong Man 2002) to get higher fish yield (an increase of 30–40% in
comparison with fish without duck integration) due to the duck manure and waste
feed. Duck houses are often built above or near the fish pond, where herbivorous
and omnivorous fish can be reared such as carp, roach and tilapia. Duck are kept
in a house at night and allowed to range freely during daylight. They scavenge
snails, crab, algae, plankton, fingerings and other available feeds in the pond.
Generally, the number of ducks can ranges from 200–300/ha. After 2–3 years, both
duck and fish yields start to decrease, since the ponds are full of sludge and
become toxic to the fish. The sludge collected from the pond is a good source of
organic fertilizer for the gardens and rice field. The third integrated model is
also applied, and is referred to research carried out by Islam et al. (2004).
They reported that thirty ducks and four fish species were introduced along with
rice. Ducks were allowed to graze during the day and then were confined in
houses built on the corner of the land. No supplement was supplied for the fish.
The rice yield was lower than the culture with fish only. However, farmers could
also benefit from the increase in the yield of fish and eggs from ducks.

Intensive duck production systems

According to Dean and Sandhu (2006), commercial duck production can be
categorized into two types: absolute confinement and semi-confinement. The
modern intensive total-confinement system is clearly differentiated by high duck
density, high capital investment for housing, commercial feed and labour (Nguyen
Thi Kim Dong 2005). Feed is supplied as well balanced rations; floor is design
to eliminate wetness, and water troughs are installed such that ducks can not
spread water. The intensive system is mainly found in agro-industrial zones or
in peri-urban areas. Exotic and improved duck breeds are commonly reared in this
system, mostly for meat. Ducks grow fast and are killed at early stage with high
productivity. To semi-confinement system, duck housing is similar to confinement
system, except that ducklings after 2-3 weeks can be allowed outdoors during the
day.

However keeping ducks is risky; diseases may kill the birds in a flock within a
few days. Due to disease outbreaks, it was a negative experience when some
farmers took out loans with high interest rates or sold land to refund and
restart with ducks. It also recognized that the duck
production in small flocks creates many challenges for outbreak control. Farmers
are keeping these flocks and even some intensive farms are unaware of
biosercurity and seek veterinary service if their poultry have health problems.
The transportation of birds should be under the government control. It is
a concern that the free-ranging system plays an important role in AI spread in
Vietnam, especially in remote areas where these are interactions between ducks
of different villages (Edan et al. 2006).

Common ducks

According to Nguyen Thi Kim Dong (2005), common ducks are crossbreds of male
Cherry Valley (imported to Vietnam since 1975) and female Pekin Ducks. Other
common ducks are crosses between male Super-Meat ducks (meat type ducks imported
from the United Kingdom in 1989) and female crossbred ducks (between Cherry
Valley and Pekin ducks). According to various studies carried out recently,
common ducks reach normal slaughter weight at around 9-10 weeks of age. Common
ducks can grow at a similar rate to the Muscovy although they consumed double
the amount of duckweed than Muscovy ducks (Men et al. 1996). Common ducks
are preferred by farmers in the peri-urban and rural areas due to their ability
to utilize low quality feed (by-products and natural forages), but the feed
conversion rate is poor (Nguyen Thi Kim Dong 2005; Bui Xuan Men et al. 1995).

However, the pure breeds are facing a problem that they are being lost. A sign
of this is that people can not recognize the difference between breeds in the
field. In the Mekong Delta, for example, ducks that are called “Tau” but now
look very close to the Khaki Campbell since the indigenous pure breeds have
become less common and have been crossed with other different breeds (Desvaux
Stephanie et al. 2008).

The nutrient requirements of ducks

Ducks can grow well, whether by scavenging or consuming a complete ration.
However, the feed offered should contain enough nutrients and balance in ration
regarding to the requirements for grow, maintenance and reproduction. Their need
can be differ, depending on the stage (age) of birds and the production purpose
(Table 1).

Feeds for ducks

Ducks are easy to raise under various management conditions. They can grow
faster and reach higher performance earlier in a commercial system (semi- or
fully-confinement), if supplied commercial feeds with balance a formula for each
development stage. These systems are now widely applied, but rarely found in
rural and remote areas where there is a lack of appropriate technologies and
financial supports. However, ducks are preferable because of their good
adaptation to local feed resources, such as household waste, agro-industrial
by-products and forages.

The Mekong Delta region is the biggest “rice basket” of the country. Annually,
rice mills produce large quantities of grain for export, as well as the
by-products (rice husk, rice bran and broken rice). The broken rice is not as
valuable as rice grain but it also can be exported or used locally for human
consumption. Rice bran is the outer layer of brown rice kernel (after separating
the husk) which is removed while milling brown rice to white. Rice bran, a rich
source of nutrients and pharmacologically active compound, is currently used as
livestock feed, and is also used for oil production (Tahira et al.2007).
According to Houston (1972), rice bran accounts for 5-8 percent of paddy rice
(whole grain). Commonly, in Vietnam, the rice mills produce three kinds of rice
bran: the initial bran (mixed with rice husk fragments) and two types of bran
produced in the polishing process which is very fine and have higher nutritional
value than the initial bran. In the Mekong Delta, rice bran is cheaper than rice
grain and broken kernels, so it is the most widely available feed resource for
duck production.

The Mekong Delta is also well-known for fish and shrimp production (Le Viet Ly
1994), thus their by-products are available in large amount. Commonly, fish meal
and soybean meal are widely used to supply protein; a good balance amino acids
are suitable for all livestock species. However, due to the increasing oil price
and the competition with human demands, local feed resources are a good
alternative in terms of convenience and maximum net profit. Recent studies have
shown that expensive feedstuffs can be replaced by alternative cheap ingredients
without reducing the feeding value. Nguyen Thi Kim Dong (2005) for example found
that soybean meal can be replaced by soya waste at up to 60% and using ensiled
shrimp waste could replace fish meal (around 20%) without any effects on the
growth performance of growing crossbred ducks, thus resulting in higher incomes
for farmers. Study carried out on meat type ducks under Vietnamese farming
conditions also showed that meat and bone meal as well as poultry by-product
meal can fully replace fish meal (Nguyen Quang Dat and Yu Y2003).

Duckweed (Lemna spp.) is easily grown in lakes, ponds and lagoons and has
a high content of organic matter and crude protein (86.0 and 40.2%,
respectively). In one experiment carried out on growing ducks, Khanum et al
(2005) found that because of the low dry matter content and low crude protein
digestibility ducks had poor growth performance, and duckweed could only
included at around 50% in duck diets without negative influences on carcass
quality. Farmers can produce duckweed in lagoons near their homesteads and/or
may collect it from natural sources as feed to their ducks. This will help to
reduce feed costs by about 50%. Nguyen Duc Anh and Preston (1997) asserted that
duckweed can be fed as non-conventional protein
source to support ducklings (5-20 days of age) growth performance. Duckweed can
be used to totally replace the soybean meal but the protein is utilized is less
efficiently than the protein in soybean because of the lower digestibility.
Nguyen Thi Hong Nhan et al. (1997) reported that Trichantera leaf meal
can be used in diets for laying ducks, hens and quails. In the case of
fattening ducks, they were given free access to fresh leaves of Trichantera
or water spinach (the basal diet including broken rice, soybean and fish
meal). The intake was around 70-80 g DM/duck/day. The authors asserted that
soybean or fish meal can be reduced by 10% if the ducks had a free access to
either Trichantera leaves or water spinach, with no negative influence on
growth performance or carcass quality.

Taro (Colocasia esculenta) in the Mekong Delta

Nutrient composition

Taro, which belongs to the Aracea family, can be cultivated or collected from
the wild in the Mekong Delta, particularly on the banks of ponds and along
rivers or canals. Some taro species (Colocasia antiquorum and
Colocasia gigantea ) which have a large corm or palatable stem can be used
for human consumption, while Xanthosoma sp., Alocasia sp. Alocasia cucullata
and Alocasia macrorrhiza
(giant taro/giant elephant ear) can be used both as food and animal feed.
Wild taro (Colocasiaesculenta) originates from India and
Southeastern Asia. It is a perennial herb 1.5 m tall, with thick stems, very
small corms, and with leaf blades of around 60 in length and 50 cm in width.
Wild taro is abundant particularly in wet lands since it is highly resistant to
pest and diseases. The wild taro leaf has a high nutritive value, with
22.5-26.3% crude protein (Malavanh Chittavong et al. 2008b; Chhay Ty et al.
2007). However, in common with other species of the Aracae family, calcium
oxalate (an anti-nutritional factor), is found in all parts of the plant,
causing irritation in the throat and mouth epithelium and indirectly affecting
the digestibility. Another constraint of taro is the high content of fibre (in
taro leaves, crude fibre is around 17.1-18.3% of DM, Chhay Ty et al. 2007 and
Malavanh Chittavong et al. 2008b).

Uses of taro as animal feeding

Taro is used for feeding livestock not only in Vietnam but also in other
tropical countries. A survey in Cambodia on taro varieties and their use
reported that taro is a common plant grown or developing naturally near the
houses, in the forests, ponds, streams and canals but farmers rarely fed taro to
their pigs because of the itchiness (Pheng Buntha et al. 2008b). Others
researchers also evaluated the use of wild taro (Colocasia esculenta) in
growing crossbred pigs (Chhay Ty et al. 2007, Nguyen Tuyet Giang 2008 and Pheng
Buntha et al. 2008a) and Mong Cai gilts (Malavanh Chittavong et al. 2008a).

Processing methods and their influence on the nutritional value of taro

A major constraint to livestock production is the lack of animal feed resources
(Kayouli and Stephen 1999). Many by-products and forages are not available
through out the year; and therefore, it needs to be stored with appropriate
processing methods.

Taro contains an anti-nutritional factor, namely calcium oxalate, which causes
irritation on contact. This substance is present in all parts of
the taro plant. Leslie and Patrick (1979) stated that the density of calcium
oxalate crystals in corms increases rapidly in the early stage, then decreases
in older and larger corms. Ravindran et al. (1996) showed that calcium
oxalate was a main factor contributing to anti-palatability and anti-nutritive
effects. Exceptions for corms that can be cooked for human consumption,
Cambodian farmers rarely use taro petioles and leaves for animal feeding. In
order to reduce the itchiness of taro caused by the calcium oxalate content,
most farmers boil taro before feeding it to their pigs or add sugar palm syrup
after boiling, while others applied salt, frying or sun drying (Pheng Buntha et
al. 2008b).

There are various ways to process taro in order to store it and reduce the
density of calcium oxalate crystal content, such as cooking, sun-drying, soaking
and ensiling (Table 2).

Table 2. Nutritional composition of taro with
various processing methods

Ensiling is a process that has been applied to preserve carbohydrate rich
materials, with or without additives (Machin 1999). The particular feature of
ensiling is the fermentation of feed with organic acids produced by bacteria.
Ensiled forages are a good feed source animals, as monogastrics can digest all
enzymically digestible components in the small intestine and fibrous materials
are fermented quickly in the large intestine then easily absorbed as nutrients.
This method is suitable and easy to apply for smallholders under tropical
conditions because it is safe, takes less investment and results in significant
incomes.

Taro (leaves or the mixture of petioles and leaves) are harvested and chopped
into small pieces. The size of the fragments depends on what type of animal is
reared. Then, taro pieces are partially sun-dried to reduce the moisture
content and packed tightly into plastic bags or containers. The bag should be
sealed tightly to prevent contamination by air. Chhay Ty et al. (2007) mixed
taro with rice bran and salt (10 kg rice bran, 0.5 kg salt and 89.5 kg taro
leaves), and the silage was stored in normal temperatures for 30 days before
being used. The purpose of this procedure was to reduce the content of calcium
oxalate. Other additives can be used to stimulate the fermentation of bacteria
and improve the palatability, such as molasses (Du Thanh Hang and Preston 2010
and Malavanh Chittavong et al. 2008a), and sugar palm syrup (Pheng Buntha et al.
2008a).

Effect of taro foliage on the growth performance of common ducks

Fresh taro leaves

The DM and CP intakes were significantly different among treatments in which
ducks were offered by basal diet with five feeding levels (3, 4, 5, 6 and 7% of
BW) and fresh taro leaves fed ad libitum. The increasing fresh taro leaves
intake was to compensate for the reduced amount of basal diet. The result is
consistent with the study carried out by Nguyen Thi Kim Dong (2005). The mineral
as well as vitamin content of the fresh taro leaves can meet the demand of
ducks, confined by the similar growth performance of confined common ducks (FCR
and ADG) between diets, with and without a premix of vitamins and minerals.

In spite of ducks being able to consume high amounts of a bulky and fibre-rich
feeds, the growth rate is poorer than if they are given a low fibre and
high-energy diet. The growth performance of ducks in the present study was lower
than of ducks fed "A" molasses substituted for broken
rice and rice polishings at 15 or 30% in the diets (Bui Xuan Men and
Vuong Van Su 1990). There was a relationship between the percentage of taro
leaves intake in dry matter intake and the length of caecum as well as the
weight of abdominal fat. The more taro leaves consumed, the less fat stored and
the longer caecum length. The fibrous bulk in the digestive tract could be the
reason for the increase in ceacum length.

Silage of taro foliage (leaves and stem)

The ensiling process applied in forages should lead to an increase in the
concentration of metabolizable energy in the diets, and therefore to improved
performance in terms of growth rate and feed conversion. In fact, there were no
differences in growth performance, but there were major effects on the carcass,
with linear decreases in carcass percentage and in abdominal fat as the level of
taro silage in the diet was increased. These responses can be considered as
positive in terms of carcass quality of the product and the opportunity to use
local available forage which grows wild in the Mekong delta.

It is apparent that the ensiled taro foliage (leaves plus stems) has a
relatively high nutritive value. The observations in this experiment do not
permit conclusions to be made as to the relative nutritional values of the leaf
and stem in the ensiled product. Rodríguez and Preston (2009) concluded that
ensiling the combined leaf and stem of New Cocoyam (Xanthosoma sagittifolium)
was a simpler process than ensiling only the leaf. When leaves were ensiled
alone a source of fermentable carbohydrate (sugar cane juice) had to be added.
However, it was found that the stem contained appreciable amounts of soluble
sugars, and thus there was no need for an additive when the leaves and stems
were ensiled together. Dao Thi My Tien et al. (2010, unpublished data) also
observed that the stems of taro (Colocasia esculenta) contained high
levels of soluble sugars (up to 40% in the DM) and that this facilitated the
ensiling process of the combined taro leaves and stems.

Conclusions

·Vietnam is an agricultural country with huge annual rice
production, so the by-product (rice bran) from mills is abundant. This is a
cheap and available feed resource for duck production.

·Taro foliage can be supplemented to local feed resources for
common ducks to bring economic benefit for smallholders in Mekong Delta.

•Live weight gain was reduced from 30 to 20 g/day, and FCR was
poorer, when the basal diet of rice bran, broken rice and SBM, was restricted to
3% of LW (as DM) with fresh Taro leaves ad libitum

•There was no effect on ADG and FCR of including a mineral-vitamin
premix when Taro leaves were also fed

•Growth rates of ducks were:

Ř The same over a range of ratios of rice bran and taro silage from
80:20 to 40:60

Ř8% higher when the feeds were given as a mixture rather than
separately

•Calcium oxalate in taro leaf-stem silage was lower than in fresh
taro leaves

•Calcium oxalate in taro leaf-stem silage was lower than in fresh
taro leaves

•Smallholders farmers in the Mekong Delta can get significant
economic benefits from fattening common ducks as using the local feed resources
(rice bran and taro foliage) that are very cheap compared with commercial feeds
and widely available in the region and are safe for ducks.

Du Thanh Hang and T R
Preston 2010: Effect of processing
Taro leaves on oxalate concentrations and using the ensiled leaves as a protein
source in pig diets in central Vietnam, from
http://www.lrrd.org/lrrd22/4/hang22068.htm